Method and system for efficient addressing and power savings in wireless systems

ABSTRACT

A method for addressing groups of stations in a wireless communication system begins by assigning the stations in the system into a number of groups. A group identifier is signaled to each station and the group identifier is indicated in a frame for each group that has data in the frame. The addressing method can be applied to power savings for the station, wherein the station enters a power saving mode if the group identifier for the station is not present in the frame.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.11/406,877, filed Apr. 19, 2006, which claims the benefit of U.S.Provisional Patent Application No. 60/674,811, filed Apr. 25, 2005,which is incorporated by reference as if fully set forth herein.

FIELD OF INVENTION

The present invention relates to wireless packet data communicationsystems in general, and in particular to a method and system forefficient addressing and power savings in wireless communicationsystems.

BACKGROUND

Frame aggregation and frame bursting are two proposed mechanisms forenhancing the performance of WLAN systems. Such mechanisms are underconsideration for the 802.11n extension to the 802.11 WLAN standard,which will allow for higher throughput WLAN devices. Both TGnSync andWWISE proposals are considering various types of frame aggregation andframe bursting schemes.

FIG. 1 shows different types of frame aggregations and frame burstingschemes that were proposed by either TGnSync, by WWiSE, or by both.Aggregation schemes can generally be differentiated according to whichparts of a packet they aggregate.

MSDU aggregation (100) aggregates one or more medium access control(MAC) service data units (MSDUs) 102 to form an aggregated MSDU (A-MSDU)104, with each MSDU separated by a subframe header 106. A MAC header 108is added to the A-MSDU to form a single MAC protocol data unit (MPDU)110.

MPDU aggregation (120) aggregates one or more MPDUs 122 to form a singleaggregated MPDU (A-MPDU) 124, with each MPDU separated by an MPDUdelimiter 126. A physical (PHY) header 128, including a legacy trainingand SIGNAL field 130 and an HT Training and SIGNAL field 132, is addedto the A-MPDU 124 to form a PHY protocol data unit (PPDU) 134.

PPDU aggregation (140) aggregates one or more PPDUs 142, each PPDUincluding a PHY header 144 and an MPDU 146. A PHY header 148, includinga legacy training and SIGNAL field 150 and an HT Training and SIGNALfield 152, is added to form a single aggregated PPDU (A-PPDU) 154.

PPDU Bursting (160), also known as high-throughput (HTP) BurstTransmission, involves transmitting a sequence of frames 162 by a singlehigh-throughput station (STA) in a single medium access. Each frame 162includes a PHY header 164, having a legacy training and SIGNAL field 166and an HT Training and SIGNAL field 168, and an MPDU 170. The frames 162may be transmitted as part of an A-PPDU, or with reduced interframespacing (RIFS) 172 to enhance medium efficiency.

Aggregation or bursting schemes can support either aggregating framesdestined to a single receiver (i.e., a single WLAN destination),aggregating frames destined to multiple receivers (i.e., multiple WLANdestinations), or both. SRA is used to refer to Single ReceiverAggregation, while MRA is used to refer to Multiple ReceiverAggregation. For example, the MSDU aggregation scheme is typically usedfor SRA since it contains only one MAC header which can identify asingle WLAN receiver address. On the other hand, the MPDU aggregation,PPDU aggregation, and PPDU Bursting schemes can either be used for SRAor MRA, since each MPDU within the aggregate or burst contains a MACheader which can identify a different WLAN receiver address.

Frame aggregation and bursting schemes have the benefit of increasingthe efficiency and overall throughput of the WLAN system. A drawback isthat most of the aggregation and bursting schemes are not presentlysupportive/friendly to the issue of saving power/battery. The mainproblem is that the duration of an aggregated frame or burst can bequite long. So if knowledge about which STAs' data (i.e., which WLANdestination addresses) are contained within an aggregated frame or burstis not provided upfront, then each STA within the WLAN will have toreceive and decode the entire aggregated frame or burst in order tocheck if the frame or burst contains some data destined to the STA.

The act of receiving and decoding the information in such lengthypackets consumes a large amount of energy for the STA's receiver, andsignificant power/battery savings can be achieved if the receiving STAhas some upfront knowledge to indicate that it should not listen to(receive and decode) a particular aggregated frame or burst if it is notan intended receiver.

By providing upfront knowledge about which STAs have data within theaggregated frame or burst, all STAs that do not have data within theaggregated frame or burst can achieve power savings by sleeping (i.e.,not listening to or not decoding the full packet) during the duration ofthe aggregated frame or burst. On the other hand, STAs that do have datawithin the aggregated frame or burst may be able to achieve powersavings if some more upfront information is provided. Such upfrontinformation concerns the timing of the transmission of the STA's datawithin the aggregated frame or burst. The basic idea is that such STAswill utilize the upfront timing information to wake up (listen anddecode) during the portion of the aggregated frame or burst thatcontains its data, and sleep during the remaining portions that do notcontain its data, hence reducing its power consumption.

In prior art, there are some proposals to support power/battery savings.For example as shown in FIG. 2, the A-MPDU aggregation scheme 200 of theTGnSync proposal proposes using an MRAD (Multiple Receiver AggregateDescriptor) as the first MPDU within an aggregated frame (A-MPDU) thatis destined to multiple receivers. The PPDU 202 includes a PHY header204 and an A-MPDU 206. The PHY header 204 includes a legacy training andSIGNAL field 208 and an HT Training and SIGNAL field 210. The A-MPDU 206includes an MRAD MPDU 212 and a plurality of MPDUs 214, each separatedby an MPDU delimiter 216.

The MRAD MPDU 212 is used in the following fashion. A STA that does nothave data within the aggregated frame will receive and decode up untilthe end of the MRAD MPDU 212, and the STA learns that its receiveraddress is not included within the MRAD, it can go to sleep (i.e.,disable its receiver) until the end of the aggregated frame. SinceTGnSync requires that MPDUs destined to the same receiver address haveto be placed contiguous to each other within the A-MPDU, a STA that hasdata within the aggregated frame will receive and decode data until itreceives all of its MPDUs and detects a different receiver address inthe next MPDU, at which point it can go to sleep (i.e., disable itsreceiver) until the end of the aggregated frame.

Even though the MRAD mechanism provides a way to achieve power savingsin the case of MRA based on A-MPDU aggregation, the MRAD mechanism isappropriate for single-rate MRA aggregation but not sufficiently suitedfor Multiple-Rate MRA (where the aggregate MPDUs are sent at differentrates), for PPDU Aggregation, nor for PPDU Bursting.

One proposal describes MMRA (Multiple-rate (or Multiple MCS) MultipleReceiver Aggregation), which relates to support for power savings thatcan be achieved when Multiple-rate MRA (MMRA) is used. That proposalincludes using an MMRAD (MMRA Descriptor) which contains information onthe STA IDs (i.e., receiver addresses) as well as timing offsetinformation, which can be used for power savings. The MMRAD is definedwithin the MAC portion of the frame, and a single bit within the PHYportion of the frame (specifically within the HT-SIG field) is used toindicate the presence of an MMRAD.

The prior art proposals suffer from many drawbacks, such as: the lengthof the MRAD or MMRAD is large and inefficient, it is a variable lengthfield, and implementation can be simplified by using only a fixed lengthpacket. Also due to such a large field, the power saving informationcannot be embedded within the PHY layer which should be maintained at asmall size. Since the power savings information is sent at the MAClevel, it is not sufficiently robust because the MRAD is sent at a ratethat not all STAs may be able to decode. It is also a MAC MPDU, so if itis lost or if a STA cannot properly decode it, then there are no powersavings. Another drawback is that timing information is not provided inan efficient manner. The current proposals mostly apply to A-MPDUaggregation, and cannot efficiently and robustly work with A-PPDUaggregation, PPDU bursting, MRMRA, or reverse direction traffic.

SUMMARY

The method is applicable to frame aggregation schemes, frame burstingschemes, and to frames that are not aggregated (i.e., those sent to asingle receiver for example). The present invention is not restricted topower and battery savings, but can also be used for other purposes, suchas for providing addressing scalability via simplified group addressing,for use in packet scheduler design or implementation, or for use invarious radio resource management functionalities.

A method for addressing groups of STAs in a wireless communicationsystem begins by assigning the STAs in the system into a number ofgroups. A group identifier is signaled to each STA and the groupidentifier is indicated in a frame for each group that has data in theframe.

A method for enabling power savings in a wireless communication systembegins by assigning the STAs in the system into a number of groups. Agroup identifier is signaled to each STA and the group identifier isindicated in a frame for each group that has data in the frame. A STAenters a power saving mode if the group identifier for the STA is notpresent in the frame, thereby saving power.

A method for enabling power savings in a wireless communication systembegins by indicating a traffic direction in a frame, the trafficdirection indicating the frame destination. The STA enters a powersaving mode if the traffic direction is not to the STA, thereby savingpower.

A method for enabling power savings in a wireless communication systembegins by receiving and decoding a frame at a STA until the STA decodesa power saving indicator. The STA enters a power saving mode if thepower saving indicator indicates that the STA can use the power savingmode.

A method for enabling power savings in a wireless communication systembegins by sending timing information to a STA in a frame, the timinginformation occupying a portion of the frame. The STA enters a powersaving mode based on the timing information. The STA exits the powersaving mode based on the timing information, and receives and decodes aportion of the frame after exiting the power saving mode.

A method for enabling power savings in a wireless communication systembegins by providing listening instructions for a frame, the listeninginstructions including an indication of how much of a frame is to bedecoded by a STA that is not an intended receiver of the frame. Thelistening instructions are included in the frame, which is transmittedto a STA. The frame is received at the STA and the listeninginstructions are decoded. The frame is decoded at the STA based on thelistening instructions, wherein the STA enters a power saving mode afterdecoding the portion of the frame indicated by the listeninginstructions, whereby the STA saves power.

A method for enabling power savings in a wireless communication systembegins by sending a first frame from a STA to an AP, including a requestfrom the STA to opt out of a transmission type. At least one secondframe is sent from the AP. The second frame is received at the STA,which decodes the transmission type of the second frame. The STA entersa power saving mode if the transmission type of the second frame is thetransmission type that the STA has opted out from.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding of the invention may be had from thefollowing description of a preferred embodiment, given by way ofexample, and to be understood in conjunction with the accompanyingdrawings, wherein:

FIG. 1 is a diagram of several existing frame aggregation and burstingschemes;

FIG. 2 is a diagram of an existing MPDU aggregation scheme using anMRAD;

FIG. 3 is a diagram of grouping STAs and group communications with anAP;

FIG. 4 is an example of using group ID information in connection withtiming information and STA sleep periods;

FIG. 5A is a diagram of a legacy PLCP header in an existing TGnSync PHYheader;

FIG. 5B is a diagram of a legacy PLCP header including a frame typeindicator;

FIG. 6A is a diagram of an existing HT-SIG field in the TGnSync PHYheader;

FIG. 6B is a diagram of an HT-SIG field including an HT-SIG_(x) field;

FIG. 7A is a diagram of existing SIGNAL-MM and SIGNAL-N fields in aWWiSE PHY header; and

FIG. 7B is a diagram of SIGNAL-MM and SIGNAL-N fields includingadditional information fields.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereafter, the term “station” (STA) includes, but is not limited to, awireless transmit/receive unit, a user equipment, a fixed or mobilesubscriber unit, a pager, or any other type of device capable ofoperating in a wireless environment. When referred to hereafter, theterm “access point” (AP) includes, but is not limited to, a basestation, a Node B, a site controller, or any other type of interfacingdevice in a wireless environment.

The present invention applies to a variety of different technologies,including aggregated frames, non-aggregated frames, reverse directionschemes, multiple responders' schemes such as MRMRA (i.e.,Multi-Response MRA), reverse direction traffic, multi-poll, and MRMRAMulti-poll (MMP). Hence, the scope of power savings as defined by thepresent invention can cover frames that are standalone, are notaggregated, or are single-receiver aggregated, all types of aggregatedframes or bursts, and all schemes that can have multiple responders oruse multi-poll.

Group Addressing of STAs

The present invention provides an efficient way of addressing groups ofSTAs. The current art schemes for addressing WLAN STAs are not efficientfor use in limited-size headers, such as the PHY (physical layer) headersince they require many bytes. Basically, the current WLAN systems andmethods do not allow for the efficient addressing of STAs at the PHY(physical) layer or even the MAC (medium access control) layer.

The present invention proposes a new efficient scheme for groupaddressing of STAs, and can be used in WLAN headers with limited size.This group addressing scheme can be used by various performanceenhancement functions, such as power saving, radio resource management,improving QoS (Quality of Service), and packet scheduling (packetscheduler design and implementation). It may also be used to uniquelyidentify the final traffic destination (e.g., the receiving WLAN STA)when the number of STAs is small enough. In a WLAN, efficient addressingcan be achieved by having an AP (access point) organize the STAs it isservicing (e.g., those STAs that are associated with the AP) intodifferent groups, with each group capable of containing multiple STAs.The terminology “Power Saving Groups”, “Station Groups”, or “AddressGroups” can be used to refer to such groups.

While a WLAN STA is typically uniquely identified by its MAC address,performance enhancements and power savings can be achieved without theneed to specify the full MAC address or parts of the MAC address of theSTA. Instead, a “group address,” a “group identifier,” a “groupindicator,” or a “group number” can be used to enable power savings. Forexample as shown in FIG. 3, assume that an AP 300 would like to organizethe six STAs (302-312) that it is servicing into four groups. Onepossibility is for the AP 300 to assign STAs #1 (302) and #6 (312) togroup 1, STA #2 (304) to group 2, STA #4 (308) and #5 (310) to group 3,and STA #3 (306) to group 4. It is also possible for the AP 300 to placeone STA in multiple groups. In FIG. 3, STAs #5 (310) and #6 (312) bothbelong to groups 1 and 3.

Once the AP 300 decides to assign a STA to one or more groups, it canuse any form of messaging to signal the assigned group or groups to theSTA. For example, when STA #6 (312) is associating with the AP 300 andonce the AP has decided to assign or classify STA #6 as part of group 1,the AP can use a management frame, action frame, control frame, or dataframe to indicate to STA # 6 that it has been assigned into group 1.Such signaling can be conducted in a variety of ways, for example, byintroducing new fields within the association or re-association frames;existing management or action frames (e.g., those used for blockacknowledgement (ACK) setup, traffic stream setup, or direct linkprotocol (DLP) setup); control frames such as ACK, block ACK request(BAR) and block ACK (BA), initiator aggregation control (IAC)/responderaggregation control (RAC), modulation coding scheme (MCS) Request andMCS feedback; and the data frames.

Some sort of ACK (feedback) may be used, whereby a STA confirms that ithas correctly received its new group assignment. The group assignmentand its subsequent confirmation (through feedback or ACK) can besignaled within any existing WLAN frame or by defining new frames. TheAP can classify itself as part of a special group on its own, as part ofno group, as part of any group that may contain other STAs, or as partof every group. The AP may also communicate its assigned group to theassociated STAs.

The AP can belong to a default group (e.g., a fixed value) that all STAsare aware of (for example, a group that is identified by all 0's or alll's; in FIG. 3, the AP belongs to group 0). A STA that has not yet beenassigned into a group by the AP can assume that it is, by default, partof all possible groups (e.g., a STA belongs to every group until it hasbeen assigned into a specific group). Also, within the specific contextof Direct Link Setup or Direct Link Protocol (DLS or DLP), the AP maycommunicate to a STA the group ID it should use when talking directly toanother STA (e.g., which could be the group that the other STA isassigned into) or alternatively a default group may be used for suchpurpose.

The groups' assignment, re-assignment, or signaling can be conducted atany point of time that the AP or STA deem necessary, and is notrestricted to specific phases such as negotiation or association. Staticassignments can also be used, whereby an operator or user configures andorganizes the STAs and AP into the necessary groups, and inputs thatinformation into the STAs or APs. Also, distributed algorithms may bedevised for assignments, whereby a STA assigns itself into a group onits own, using no or little explicit communication/signaling.

Multi-dimensional groups can be defined, which can be interpreted ashaving sub-groups within groups. For example, a STA can be assigned togroup 1 and sub-group 2. The sub-group concept can be useful todifferentiate between the multiple STAs that belong to the same group.For example, if group 1 contains three STAs and there are four availablesub-groups within group 1, each of the three STAs can be put into adifferent sub-group, thereby providing further differentiation betweenthe STAs within the group. Therefore, a more general case is to assignto a STA one or more values, with each value representing a group, asub-group within a group, and sub-sub-group within a sub-group, etc. Themore general case is to have N dimensions of groups, which can beidentified by the N-tuple (g1, g2, . . . , gN), and a STA will beassigned N values, one value for each of the N dimensions (i.e., acombination of groups).

Groups may also be defined by taking into account other characteristics.For example, one group could identify that broadcast traffic iscontained within the frame and will effectively contain all STAs withinthe AP coverage area. If the AP would like to send an aggregated framethat contains broadcast traffic and traffic belonging to group 2, it canuse group 0 to indicate that there is broadcast traffic destined to allSTAs, and can use group 2 to indicate that there is traffic for at leastone STA in group 2. This concept is especially useful when the datawithin the aggregated frame is ordered by traffic type; for example,broadcast traffic and/or multicast traffic is placed before unicasttraffic within the aggregated frame. A broadcast group can be used torepresent that the data type is broadcast traffic destined to all STAs.

Similar concepts can apply for multicast traffic, by having one or moregroups indicating multicast traffic. One group can indicate that both oreither of broadcast and multicast traffic is present within the frame(i.e., a single group to represent both broadcast or multicast). Theframe type information can be used in defining the groups. For example,one group may be used for management, action, or control types offrames. Additionally, QoS related information can be used when definingthe groups.

There are many possible algorithms that can be used for organizing theSTAs and/or different traffic types into the available groups. Onealgorithm is to use a subset of the bits of the index of the memorytable (e.g., the RAM table) where the entry containing the MAC addressof the STA is located. Since an AP probably maintains a lookup table ofits associated STA's MAC addresses, the AP can use the Least SignificantBits of the table index where a STA MAC address is stored in RAM. Asecond algorithm is to apply a hashing function on the MAC address ofthe STA (as well as other characteristics of the STA and traffic ifdesired). A third algorithm is to monitor (measure) the load (i.e.,traffic utilization) on each of the groups (or their STAs), anddynamically change the group assignment in such a way that will producea nearly equal load among all groups. A fourth algorithm selects theleast utilized group (in terms of traffic utilization) to assign to anewly associated STA. Other algorithms include attempting tosplit/balance the load/usage among all groups, and may take into accountother factors, such as packing/grouping those STAs that have similarframe aggregation requirements, use similar data rates or power levels,or have similar QoS or radio resource management requirements, withinthe same group.

Signaling the Group Assignment Information

As described previously, management, action, control, or data frames canbe used for signaling the assigned group to a STA, the group of anotherSTA, or the AP's group. For example, IAC/RAC, RTS/CTS, MCS request andfeedback, BAR/BA, Association/Re-Association Request and Responseframes, or CF-Poll or QoS Poll, could be used for such signalingpurposes. The signaling may consist of a group assignment message whichcontains a flag to indicate that this is a group assignment message, anda value (encoded as a bitmap or in other form) of the newly assignedgroup or groups. The assignment message may also contain information onthe scope of the assigned group or groups, for example, whether theassigned group is applicable for this STA, for the AP, or for anotherSTA (e.g., when doing DLP).

Once a STA correctly receives a group assignment message, it may confirmvia a group ACK message back to the AP that it has correctly receivedand accepted the newly assigned group or groups. Alternatively, the STAcan periodically confirm in an unsolicited manner the group or groups itis using for each of the different communication scopes, by sending agroup confirmation or ACK message.

Re-Assigning STAs to Different Groups

A STA can also request a group re-assignment, if it is not satisfiedwith the group it is currently assigned to. For example, a STA measuresits battery level, and if it is short on power (i.e., when certainthresholds are crossed), it can tell the AP via a message that it is lowon power, and that it would like to request a group re-assignment. TheSTA may specifically include a measure of its battery power level withinsuch request. Upon receiving the message, the AP may decide to deny oraccept the STA's request and may assign the STA into a new group. A STAcan indicate to the AP during a negotiation, setup, or any signalingphase, via a management, action, control, or data frame, whether or notit has the capability to use the power saving group information for thepurpose of saving power, since such indication can be helpful for the APin designing and organizing its groups.

Power Saving Group Information

The information proposed for use in realizing power savings, insimplified or scalable addressing, in scheduling frames (schedulerimplementations), for any radio resource management functions, or forany other performance enhancement functions, is generically referred toas “power saving group information”. The use of such information is notrestricted to power savings, but can be used for other purposes, such asdata scheduler implementations; grouping STAs with similar aggregationrequirements (i.e., those frames that are likely to be aggregatedtogether), similar data rate, similar power, or similar QoS requirementswithin the same group; and various radio resource management functions.Some or all frames usable by the WLAN can contain all or some pieces ofthe power saving group information within the frame header (PHY or MACheader), the body of the frame, or any previously sent frames (e.g.,RTS/CTS, IAC/RAC, CF-Poll, or QoS-Poll). The power saving groupinformation can consist of one or more of the following pieces ofinformation.

Presence or Validity Flag (PVF)

A field (or bit) used as a flag (herein referred to as a flag) toindicate whether at least one piece of the power saving groupinformation is present in the frame (e.g., within the frame header). Forexample, the PVF can be used to indicate whether there is power savinginformation within the frame or not. In the case where every frame issupposed to contain the power saving information, such a flag may not benecessary. The flag may be used for implementing variable-length PHY orMAC header fields or headers.

For example, the flag can indicate whether an extended portion of theheader is present or not, wherein the header extension contains all orsome power saving information. A bit can be used within the SIGNAL fieldof the PHY header (e.g., within the HT-SIG field or the SIGNAL-N field)to indicate that one (or more) additional OFDM symbols is providedwithin the HT-SIG field, and such additional OFDM symbols contain fieldsthat provide all or some power saving information. In another variant,the flag can be used to indicate the availability or validity of thepower saving information fields that are contained within the usual(mandatory) OFDM symbols of the SIGNAL field, without the need for anextra OFDM symbol. Another use of the PVF (e.g., by using another bit)may be to indicate if the power saving group information is valid ornot.

Group Presence (or Absence) Indicators (GPI)

A frame contains information that identifies the group or groups of STAsthat the frame is destined to. The GPI is applicable to standaloneframes, aggregated frames, a burst transmission, or a sequence offrames. For example, one form of specifying and encoding the GPIinformation is by using a bitmap (or a mask). Returning to thepreviously described four groups example, the GPI field can be definedas the bitmap consisting of four bits (b1, b2, b3, b4), whereby thevalue of b2 indicates whether the frame contains data for at least oneSTA assigned into group 2. To illustrate, when an AP sends data to asingle STA that is part of group 2, the AP can use the bitmap 0100 toindicate that a STA belonging to group 2 has some data present in thesent frame, while such frame contains no data belonging to the otherthree groups.

Alternatively, the group can be defined using regular encoding (e.g.,10), to indicate that this frame includes data destined to a STAbelonging to group 2.

As another example, when an AP sends data to STAs using an aggregatedframe (e.g., when using MSDU aggregation, MPDU aggregation, PPDUaggregation, PPDU Bursting, MRMRA, or Multi-Poll), a bitmap value of0110 indicates that the frame contains data for at least one STA ingroup 2 and at least one STA in group 3, and that the frame does notcontain data for group 1 or group 4. It is noted that even though thisexample assumes four groups, any number of groups can be used and thebitmap is expanded to accommodate the number of groups used. Further,the number of groups used can be presented as a dynamic variable. TheGPI can be contained within the frame header, the PHY header, the MACheader, the SIGNAL field (legacy SIGNAL, HT-SIG, or SIGNAL-N) of the PHYheader, the MAC header, the MRAD, an MMP, or any multi-poll frame.

Group Timing Information (GTI)

In the case of multiple-receiver aggregation, providing GTI can lead tohigher power savings for those STAs that are aggregated within a frame.GTI may not be needed by STAs which are not part of the aggregatedframe, since they can still achieve power savings by using the GPI.

To illustrate how GTI can be used, consider the previous example wherethe bitmap value 0110 was used to indicate that the aggregated framecontains data for at least one STA in group 2 and at least one STA ingroup 3. Assuming that the data for a given group is contiguous withinthe aggregated frame, timing information can be provided whichidentifies the time at or near which group 2's data will start beingtransmitted, and also identifies the time at or near which group 3'sdata will start being transmitted.

The GTI allows a group to sleep (i.e., not receive or decode) the datauntil the time at which the first piece of data for that group istransmitted, hence achieving power savings in between. The power savingsmay be attained since the receiving STA can sleep once it receives itsdata and detects a change in receiver address in the next piece of datain the aggregated frame.

In order to provide the GTI, the start time for each group within theframe (e.g., in the form of a time offset) is provided. This informationis the time at or near which the first piece of data belonging to anySTA within the group starts getting transmitted. In order to provide theGTI efficiently, instead of fully specifying (encoding) the individualgroup start times (or offset times), a base duration (i.e., base period)that applies to all groups can be used and a different fractional valueto identify the start time (e.g., the time offset) can be used for eachgroup. For example, assuming that the base duration is 16 time units,then by using two bits, the group start time could be encoded andcommunicated as the fraction ¾, which means that the group start time(e.g., the group time offset) is (¾×16=) 12 time units either from areference point in time.

The base duration information can be derived from existing fields withinthe WLAN frame header. For example: the RATE and LENGTH fields withinthe Legacy SIGNAL field of the PHY header; the HTLENGTH and the MCSfields within the HT-SIG (SIGNAL) of TGnSync's frame header; or theLength and Config fields within the SIGNAL-N (SIGNAL) field of WWiSE'sframe header can be used to derive the base duration information. Thebase duration can be the same as the Spoofed Duration that is derivedfrom the PHY header information. Using the Spoofed Duration (or anyvariant that can be derived from it) as the base duration can provide anefficient method for encoding the timing (e.g., offset) information.Alternatively, the MAC header's DURATION/ID field can be used to derivethe base duration information.

An example of using the timing information based on the Spoofed Duration(SD) and GTI coding is shown in FIG. 4. The GTI indicates when the STAshould begin listening to the medium, and in FIG. 4 the coded GTI isgiven in ¼ intervals of the SD. The coding for the GTI used in FIG. 4 isdescribed in Table 1. It is noted that while Table 1 describes the GTIcoding in terms of the SD, any type of frame duration can be used toencode the GTI.

TABLE 1 Example of GTI coding GTI value When the STA begins listening 00at the beginning of the SD 01 at ¼ of the SD 10 at ½ of the SD 11 at ¾of the SD

A new field could be added to the PHY or MAC headers of the WLAN frame,specifically for the purpose of specifying the base durationinformation. The base duration can correspond to either the fullduration of the frame or a partial duration of the frame. In the case ofPPDU bursting or PPDU aggregation, the base duration can be defined asthe full duration of the PPDU burst (i.e., the base duration coveringmultiple frames) or the aggregated PPDU frame, in addition to definingthe base duration as the duration of a single PPDU (or frame).Similarly, in MRMRA, reverse direction traffic, multi-poll, or MRMRAschemes, the base duration may cover the whole duration of the sequenceof frames being exchanged.

Aside from the base duration information, the fraction value for eachgroup needs to be specified. The fraction value is multiplied by thebase duration to obtain the actual transmission start time for the group(e.g., the transmission time offset for the group). Assuming a fixedreference denominator, then only the numerator's value need to bespecified and communicated. For example, assuming a denominator of four,then two bits could be used to provide the GTI.

Again taking the example of a GPI of 0110 indicating that groups 2 and 3are present, one possible way to encode the GTI is to have two bits pergroup, so the GTI consists of eight bits (b1, b2, b3, b4, b5, b6, b7,b8), whereby the value of bits b1 and b2 provide the numerator value forgroup 1 (which may not be necessary in this example, since GPI indicatesthat group 1 is not present), while b3 and b4 provide the numeratorvalue for group 2, and so on. As an example, in order to obtain the timeoffset information at or near which group 2's transmission will start,one has to multiply the base duration by the value of ‘b3 b4’ and divideby four. The time offset information is generally interpreted as thetime at or near which a STA will start listening to the frame, when suchframe contains data for that STA (i.e., when the STA's group is presentwithin the frame).

The GTI can be contained within the frame header; the PHY header; theMAC header; or the SIGNAL field (legacy SIGNAL, HT-SIG, or SIGNAL-N) ofthe PHY header, the MAC header, the MRAD, the MMP, or any multi-pollframe. The GTI does not have to be contained in the same location as theGPI. For example, the GPI can be included within the PHY header, whilethe GTI can be included within the MAC header (e.g., within the MRAD orMMP).

Group Presence and Timing Information (GPTI)

Even though GTI and GPI information has been defined as two separatefields, they can be merged together and define the two types ofinformation within one field (GPTI), by encoding both the presence andtiming information using a pre-defined mapping. There are various waysof encoding the two pieces of information together, as shown in FIG. 4and in Table 2.

TABLE 2 Example of GPTI coding GPTI value When the STA begins listening00 at the beginning of the SD 01 at ¼ of the SD 10 at ½ of the SD 11 atthe end of the SD

With the values 01, 10, and 11, the STA can sleep until it is time tolisten to the medium, thereby saving power. The special case of a 11 canindicate that the group is not present, since the STA will startlistening at the end of the SD and will sleep throughout the whole framebody transmission. The GPTI can be contained within the frame header,the PHY header, or the MAC header. The GPTI can be contained within theSIGNAL field (legacy SIGNAL, HT-SIG, or SIGNAL-N) of the PHY header, theMAC header, the MRAD, the MMP, or any multi-poll frame.

AP Color (APC), Cell Color, or AP Coverage Area Color

In a system where there are multiple APs that may use the same frequencychannel, it is possible for STAs within a given cell (i.e., an APcoverage area) to listen to frame transmissions occurring in anothernearby or adjacent cell. In order to extract better power savingsperformance in such cases, the WLAN frame can contain an APidentification, which can be referred to as an “AP color” or “AP Group”or “Cell Color” or “Cell ID”. The AP color (APC) is not necessarily aunique identification of the AP. For example, if AP1, AP2, and AP3 areclose to each other and are using the same frequency channel, then byusing two bits to identify APC, AP1 can be assigned a color of 11, AP2 acolor of 01, and AP3 a color of 00. The APC can be contained within theframe header, the PHY header, the MAC header, the SIGNAL field (legacySIGNAL, HT-SIG or SIGNAL-N) of the PHY header, the MRAD, the MMP, or anymulti-poll frame.

STAs that are being serviced by AP1 will be able to save power by notdecoding further information in frames that contain a different APC inthe frame header (e.g., STAs associated with AP1 save power by notlistening to or decoding frames that contain 00, 01, or 10 as theirAPC). The APC can lead to further power savings at the multi-AP systemlevel, but even without it, power savings can still be achieved usingthe previously described methods.

Listening Directions or Instructions (LDI)

Listening Directions or Instructions (LDI) describe what needs to beread, decoded, or interpreted. In some cases, a WLAN STA that is not anintended receiver of the frame (i.e., whose data is not contained withinthe frame) may still need to read and decode the frame in order toextract certain information. For example, the STA may need to update itslocally stored NAV Duration value, and for that it may need to decode asfar as the Duration/ID information in the MAC header of the frame.Alternatively, the STA can rely on the information of the PHY header(e.g., LENGTH and RATE, MCS, or Config fields) to update its NAVDuration values.

The sender of the frame can specify using a field (e.g., a bit or fewbits) in the header whether the receiving STA is required to read anddecode all or some of the MAC header information even if it is not theintended receiver of the frame. The sender can also specify usinganother field whether a receiving STA shall update its locally storedNAV Duration value based on the information contained in the legacy PHYheader (e.g., the legacy SIGNAL field), in the high throughput (i.e.,802.11n) PHY header, or in the MAC header (e.g., Duration/ID field ofthe MAC header).

Some implicit rules can be used to derive whether the Duration/ID fieldof the MAC header (or the whole MAC header in general) needs to be reador not. One rule compares the spoofed duration using the legacy PHYSIGNAL field with the spoofed duration using the high-throughput PHYHT-SIG (or SIGNAL-N) field. If there is a certain amount of differencebetween the two, then that difference could be interpreted as anindication to read and decode further into the MAC header.

Also, as an explicit LDI, a field (e.g., one bit) within the PHY headercan indicate whether a STA can sleep immediately, or shall not sleep butkeep listening until it decodes the first MAC header (or some pieces ofMAC information) and then sleep. Such explicit instructions regardinghow far to listen into the frame can be further extended to provideinstructions on where/when (e.g., at what event/field or at what time)to stop listening: e.g., immediately, ASAP, after decoding the MACheader, after decoding the first MPDU, after decoding the MRAD, etc.

Traffic Direction

Power savings may also be obtained by knowing the direction of thetraffic. For example, if a given STA is sending traffic to the AP, itmarks in the frame header that the data is destined to the AP. STAs canuse this information to achieve power savings since they can sleepduring other STA's transmissions to the AP, by looking at this “trafficdirection” (TD) field or bit. Within the MAC header, and morespecifically within the Frame Control field of the MAC header, there are“To DS” and “From DS” fields that can be used to identify the directionof the traffic. Such information can also be used for the purpose ofachieving power savings. Additionally, a new TD field can be located inthe PHY header of the frame for the specific purpose of identifying thedirection of the traffic. The TD field can be located within the SIGNALfield (legacy SIGNAL, HT-SIG, or SIGNAL-N) of the PHY header. Theadvantage of this simple scheme is that it does not require specific newsignaling to establish the groups (one group consists of the AP as thereceiver, while the other group consists of all STAs as receivers).

Opting Out of Aggregation and Bursting Schemes

A STA can signal to the AP that it prefers not to be part of certainschemes that can make the STA consume too much power, such as a specificaggregation or bursting scheme or schemes, thereby contributing to powersavings for the STA. For example, the STA can indicate using a frame (amanagement, action, control, or data frame) that it does not want datadestined to it to be part of an aggregated frame. If the AP agrees tosuch a request and confirms agreement back to the STA, then the STA cansave power by sleeping when it detects that a frame is making use ofcertain schemes. For example, upon detecting that a frame is aggregated(by using information in the SIGNAL field, e.g. HT-SIG field) the STAcan sleep during the aggregated frame.

The STA can signal using a frame that it does not want data destined toit to be part of specific types of aggregation, such asmultiple-receiver aggregation (MRA). In that case, the STA can sleepduring frames that contain multiple receiver aggregates. Similarly, aSTA can request that it does not want data destined to it to be part ofMPDU or PPDU aggregation, but that it agrees to be part of MSDUaggregation. Some fields in the frame header (e.g., in the SIGNAL field)can be used to indicate the exact type of aggregation scheme(s) that theframe contains. A STA can sleep for the duration of a frame once itdetects that it is not supposed to listen to the frame since the framewill not contain the STA's data. A STA can negotiate whether it supportsor prefers the reception of aggregated frames (to multiple destinationsor a single destination). A STA can perform the negotiation by sendingthe information as part of a feature list, a capability list, or apreference list via a management, action, control, or data frame. TheSTA can send this frame before association, immediately afterassociation, at some later time after association, or at any other time.

The message can also be generated dynamically, for example by having theSTA monitor its battery level and upon crossing certain thresholds andsending a request to the AP to be excluded from schemes that are morepower costly (e.g., certain aggregation schemes). The STA may alsoindicate the amount of its remaining power within the message, and whattypes of aggregation schemes it prefers to be excluded from oralternatively included in.

Frame Type Indicator

The use of the unused reserved bit within the Legacy PHY SIGNAL field(L-SIG) may also be utilized as a flag for identifying non-legacy frametransmissions, such as 802.11n frames. This field can be used forenabling power savings for new implementations (new releases) of legacydevices, since STAs can sleep during those frame transmissions that arenon-legacy (e.g., during 802.11n frame transmissions).

Sleep Timer

In order to prevent a deadlock situation, in which a STA remains asleepfor a long period due to an erroneous condition, a timer mechanism canbe implemented at the STA which starts when the STA enters a sleep mode.If the STA is sleeping for more than a predetermined time period (aconfigurable parameter), it will wake up upon expiration of the timerand start listening to the medium again, since it may have been in adeadlock condition.

Location of the Power Saving Group Information

Any piece of the power saving group information (PSGI) can be includedwithin any type of WLAN frame, and within any part of the WLAN frame.PSGI can be included within the PHY header (e.g., the SIGNAL field), theMAC header, the body of the frame, or the tail of the frame. Some piecesof the PSGI can be included in a certain location in the frame (e.g.,within the PHY header), while some other pieces of the PSGI can belocated elsewhere in the frame (e.g., within the MAC header).

For frames that are part of a PPDU aggregate or PPDU burst, the PSGI canbe included in the middle of the aggregated frame or burst, for examplein the middle frame's PHY signals (headers), MAC signals (headers),mid-ambles, or delimiters. Also, for schemes such as MRMRA, reversedirection traffic, multi-poll, and MMP, some pieces of the PSGI can beincluded in the WLAN frames and in the MRAD or MMP. Adding some of theproposed PSGI in such schemes can increase their efficiency (forexample, via efficient encoding of timing information) and potentiallyimprove their performance.

FIG. 5A is a diagram of a legacy PLCP header 500 in an existing TGnSyncPHY header. The PLCP header includes a rate field 502, a reserved field504, a length field 506, a parity field 508, and a tail field 510.Because the PLCP header 500 is located early in a frame, it would be anefficient location (in terms of power savings for a receiving STA) forone of the PSGI fields.

FIG. 5B is a diagram of a legacy PLCP header 550 including a frame typeindicator field 552. The fields 502 and 506-510 are the same as in theheader 500. As the frame type indicator is one bit and the PLCP headerhas one reserved bit, the PLCP header is a suitable location.

FIG. 6A is a diagram of an existing HT-SIG field 600 in the TGnSync PHYheader. The HT-SIG field 600 includes an HT-SIG1 portion 602 and anHT-SIG2 portion 604. The HT-SIG1 portion 602 includes a length field610, a reserved field 612, and a MCS field 614. The HT-SIG2 portion 604includes an advanced coding field 620, a first reserved field 622, asounding packet field 624, a number HT-LTF field 626, a short GI field628, a second reserved field 630, a scrambler initialization field 632,a 20/40 bandwidth field 634, a CRC field 636, and a signal tail 638.

FIG. 6B is a diagram of an HT-SIG field 650 including an HT-SIGx portion652; the HT-SIG1 portion 602 and the HT-SIG2 portion 604 are the same asin the HT-SIG field 600. The HT-SIGx portion 652 includes a frame typeindicator field 654, a traffic direction field 656, a PVF 658, an LDIfield 660, a GPI/GTI/GPTI field 662, an AP color field 664, and a CRC666. It is noted that while the HT-SIGx portion 652 is shown with all ofthe PSGI fields, the HT-SIGx portion 652 can be constructed with anynumber of the PSGI fields without affecting the performance of thepresent invention. In addition, the order of the PSGI fields shown ismerely exemplary, and one skilled in the art could rearrange the orderof the fields without affecting the operation of the invention.

Alternatively, the reserved field 612 in the HT-SIG1 portion 602 and thefirst reserved first 622 and second reserved field 630 in the HT-SIG2portion 604 can be used for the PSGI. The PSGI fields can be spread outand placed into the reserved fields in their present locations, or thereserved fields could be rearranged to form a contiguous space for thePSGI fields.

FIG. 7A is a diagram of an existing SIGNAL-MM field 702 and an existingSIGNAL-N field 704 in a WWiSE PHY header 700. The SIGNAL-MM field 702includes a rate field 710, a reserved field 712, a length field 714, aparity field 716, and a tail field 718. The SIGNAL-N field 704 includesa first reserved field 720, a configuration field 722, a length field724, an LPI field 726, a second reserved field 728, a CRC field 730, atail field 732, and a service field 734.

FIG. 7B is a diagram of a SIGNAL-MM field 752 and a SIGNAL-N field 754in a WWiSE PHY header 750. The PSGI fields can be placed in the existingreserved fields 712, 720, and 728. As shown in FIG. 7B, a frame typeindicator field 756 can be placed in the SIGNAL-MM field 752, and someof the other PSGI fields can be placed in the SIGNAL-N field 754 atlocations 758 and 760. It is noted that the fields 758 and 760 could berearranged in the SIGNAL-N field 754 to for a contiguous space for thePSGI fields.

Verifying Power Saving Group Information

The integrity (correctness) of the power saving group information can beprotected via a checksum (e.g., CRC) or parity computation. The CRC canbe a newly defined field within the frame header, or can be an existingchecksum or CRC field (e.g., the CRC within the HT-SIG or SIGNAL-Nfield) within the PHY or MAC headers. The CRC can be derived solely fromall or parts of the power saving group information, or can be derivedfrom some other information within the frame header as well as the powersaving group information.

Even though most of the descriptions and examples spoke of aggregatedframes, all such descriptions and examples can similarly apply to aburst of frames or a sequence of frames, as in PPDU Bursting, MRMRA,Polling, Multi-Poll, or Multi-Poll MRMRA schemes.

The inventions disclosed herein are applicable to any WLAN systemcontext, such as BSS, ESS, IBSS, to WLAN mesh networks, and to WLANad-hoc networks. The small difference within such networks and the onegenerally described and used as an example is that if the AP is notpresent as a node within such networks, then any STA can provide thefunctionalities which were attributed to the AP. It is also possiblethat many WLAN STAs cooperate together in order to realize the functionsand methods of the inventions, without needing an AP.

The present invention is not limited only to WLAN systems or networks,or only 802.11-based WLAN systems. The invention can be used and appliedin any wireless communication system, such as other WLAN technologies orstandards, as well as in other cellular communication systems, includingUMTS, WCDMA, CDMA2000, HSDPA, HSUPA, or 3GPP LTE. The invention can alsoapply and be used in wide area wireless networks, such as 802.16.

1. A method for enabling power savings in wireless communicationscomprising: assigning stations to a number of groups; signaling a groupidentifier to each station; indicating the group identifier in a framefor each group that has data in the frame; and entering a power savingmode by one of the stations on a condition that the group identifier forthat station is not present in the frame.
 2. The method according toclaim 1, wherein the assigning includes assigning the stations based onapplying a function to a medium access control address of each station.3. The method according to claim 2, wherein the function is a hashingfunction.
 4. The method according to claim 1, wherein the assigningincludes any one of: assigning the stations based on respective mediumaccess control addresses; assigning the stations based on a trafficutilization value of each station; assigning the stations based on frameaggregation requirements; assigning the stations based on data rate;assigning the stations based on power level; assigning the stationsbased on quality of service requirements; assigning the stations basedon application requirements; assigning the stations based on radioresource management requirements; or assigning the stations into morethan one group.
 5. The method according to claim 1, wherein thesignaling includes sending a message to a station, the messagecontaining the group identifier.
 6. The method according to claim 5,wherein the message is any of: initiator aggregation control frame,responder aggregation control frame, ready to send frame, clear to sendframe, modulation coding scheme request frame, modulation coding schemefeedback frame, block acknowledgement request frame, blockacknowledgement frame, association request frame, association responseframe, re-association request frame, re-association response frame,contention-free poll frame, or quality of service poll frame.
 7. Themethod according to claim 5, wherein the message is a group assignmentmessage.
 8. The method according to claim 1, wherein the indicatingincludes any of: using a field in the frame to include the groupidentifier; or using a field in the frame to indicate which groups donot have data in the frame.
 9. The method according to claim 8, whereinthe field includes a bitmap, the position of each bit in the bitmapidentifies a group number, and the value of the bit indicates whetherthe group has data in the frame.
 10. The method according to claim 1,wherein the station remains in the power saving mode for at least aportion of the frame.
 11. The method according to claim 1, furthercomprising: receiving a request from a station to be re-assigned to adifferent group.
 12. The method according to claim 11, wherein therequest is received on a condition that the station indicates a lowpower condition.